When Mexico won a corner kick Monday at about the 70-minute mark, fans who know the numbers would not have expected much. Corner kicks have an expected goal value of around three percent. If Mexico were to break the deadlock, it would probably not happen right at that moment. But Rafael Marquez went unmarked at the top of the six-yard box and drilled his header past the Croatian keeper. Just ten minutes later, there was another Mexican corner. This was taken near-post, where Marquez flicked on a headed pass to Javier Hernandez at the back post for an easy finish. Mexico took nine corners in the match and scored two goals, for a conversion rate more than seven times the expected level.

While Mexico’s performance is a clear outlier, corner kicks have been unusually productive at the World Cup. There have been sixteen goals scored off 358 corners, compared with an expected tally of 10 or 11 goals from that many corner kicks.

In particular, we have seen a bounty of goals assisted directly by corners. Marquez’s clutch header was already the 10th World Cup goal assisted by a corner kick. The conversion rate of shots off corners is 10 out of 45 or about 22 percent. In the big four European leagues this last season, shots directly assisted by corners were converted at a rate of 13 percent.

In all likelihood, then, this World Cup’s bevy of goals off crosses is just a conversion rate fluke. A few more attackers have made the right jump at the right time and put their best contact on the ball. The Rafa Marquezes deserve credit for their quality strikes, but this is not a pattern we should expect to continue.

Now, it could be suggested that this is not merely random variation. Perhaps attacking teams have practiced their best set-play routines. Perhaps the defenses are poorly drilled or just too tired in the heat to leap effectively. If either of those explanations were correct, we would expect to see higher rates of goals not only off corner kicks, but also off all set plays. So we can test these hypotheses against the data.

In fact, crosses of free kicks have been unproductive at the World Cup.

There have been only two goals directly assisted by a set piece cross, and just one goal scorer. Ecuador’s Enner Valencia headed home both set piece goals, one early against Switzerland and the other in his side’s comeback against Honduras. The conversion rate on free kick crosses is running well under 2 percent, where in league soccer it tends to sit around 2.5 percent.

It should be noted here that this does not include all shots and goals off set pieces. Oscar Duarte’s goal against Uruguay was directly assisted by a free kick, but the pass was not a cross. My database does not allow me to isolate free kick passes that are not crosses, and so I have focused just on free kick crosses.

So the World Cup statistics on free kick crosses are not significantly out of line with the numbers observed in European league soccer in 2013-2014. While corner kicks have led to a good number of goals, other dead ball plays have not been breaking down opposing defenses nearly so effectively. Mexico’s performance Monday is unlikely to be replicated as the World Cup continues, and the conversion rate on corner kicks is likely to regress to the mean.